Psyllium

Psyllium /ˈsɪliəm/, or ispaghula (isabgol) /ˌɪspəˈɡuːlə/, is the common name used for several members of the plant genus Plantago whose seeds are used commercially for the production of mucilage. Psyllium is mainly used as a dietary fiber to relieve symptoms of both constipation and mild diarrhea, and occasionally as a food thickener.[1] It is commonly used as a food ingredient in manufactured breakfast cereals which may contribute to a healthy lifestyle by improving blood cholesterol levels and gastrointestinal function.[2]

For the town of ancient Bithynia in Asia Minor, see Psyllium (Bithynia).
Psyllium husk

Use of psyllium in the diet for three weeks or longer lowers blood cholesterol levels in people with elevated cholesterol,[2][3] and lowers blood glucose levels in people with type 2 diabetes.[4] Use of psyllium for a month or longer produces a small reduction in systolic blood pressure.[5]

The plants from which the seeds are extracted tolerate dry and cool climates and are mainly cultivated in northern India.

Uses

Dietary supplements containing psyllium are sold under brand names such as Metamucil (in the United States and elsewhere) and Fybogel (in the United Kingdom).

Constipation

Psyllium is mainly used as a viscous, soluble dietary fiber that is not absorbed by the small intestine. The purely mechanical action of psyllium mucilage is to absorb excess water while stimulating normal bowel elimination. Although its main use has been as a laxative, it is more accurately regarded as a dietary fiber and as such can help reduce the symptoms of both constipation and mild diarrhea. The laxative properties of psyllium are attributed to the fiber: it absorbs water and subsequently softens the stool. It increases flatulence (gas) to some degree.[6]

High blood cholesterol

In 1998, the U.S. Food and Drug Administration approved a health claim on food labels for dietary psyllium as a soluble fiber – if consumed chronically – that would reduce the risk of heart disease by lowering blood cholesterol.[7] Clinical research demonstrated that seven grams or more per day of soluble fiber from psyllium seed husk would sufficiently lower total cholesterol and low density lipoprotein cholesterol in people with hypercholesterolemia, two accepted biomarkers for risk of coronary heart disease.[8] The findings were later confirmed in a meta-analysis that incorporated more evidence.[9] To be eligible for the FDA-allowed health claim, one serving of a manufactured food or dietary supplement must contain at least 1.7 g of psyllium as soluble fiber.[7] Whole oats, barley and foods containing beta-glucan soluble fiber were included as eligible sources for the label claim.[7]

Type 2 diabetes

In 2014 the U.S. Food and Drug Administration approved a Qualified Health Claim (QHC) for psyllium being a benefit for people with diabetes. Any company wishing to use this QHC must use the FDA-approved wording on the label: "Psyllium husk may reduce the risk of type 2 diabetes, although the FDA has concluded that there is very little scientific evidence for this claim." [10] A meta-analysis published after the FDA decision reported that psyllium provided before meals improved fasting blood glucose and glycated hemoglobin (HbA1c), but that the larger effect was seen in people diagnosed with and being treated for type 2 diabetes, and only a modest improvement for people classified as pre-diabetic.[4] The European Food Safety Authority - responsible for reviewing health claim proposals for the European Union - has no record of having considered a psyllium health claim for glucose management.

Food

Psyllium has been used as a thickener in ice cream and other frozen desserts. A 1.5% weight/volume ratio of psyllium mucilage exhibits binding properties that are superior to a 10% weight/volume ratio of starch mucilage. The viscosity of psyllium mucilage dispersions are relatively unaffected between temperatures of 20 and 50 °C (68 and 122 °F), by pH from 2 to 10, and by salt (sodium chloride) concentrations up to 0.15 M.

Veterinary medicine

Psyllium fiber dietary supplements are used in veterinary medicine to treat sand impaction in horses to aid in elimination of sand from the horse's colon.[11]

Adverse effects

Fiber generally has few side effects.[12]

  • Psyllium can cause bowel obstructions or bezoars, if taken without adequate amount of water.[13][14]
  • Gas or stomach bloating may also occur.[12]
  • Choking is a hazard if psyllium is taken without adequate water as it thickens in the throat.[15]

Allergy

Psyllium can cause allergic reactions, including anaphylaxis.[16] Psyllium may act as a potent inhalant allergen capable of eliciting asthma symptoms.[17] Health care professionals at geriatric care hospitals, who are frequently exposed to psyllium in the laxatives administered to patients, are commonly IgE sensitized to psyllium (13.8%), and 8.6% have clinical allergy to psyllium.[18] Pharmaceutical manufacturing employees who have been exposed to psyllium during the processing have developed occupational asthma and IgE sensitization.[19] In order to protect sensitized workers, psyllium has an extremely low occupational exposure limit of 150 ng/m3.[20]

Mechanism of action

The soluble fiber in psyllium is the polysaccharide heteroxylan, a hemicellulose.[21]

Psyllium is produced mainly for its mucilage content. The term mucilage describes a group of clear, colorless, gelling agents derived from plants. The mucilage obtained from psyllium comes from the seed coat. Mucilage is obtained by mechanical milling (i.e. grinding) of the outer layer of the seed. Mucilage yield amounts to about 25% (by weight) of the total seed yield. Plantago-seed mucilage is often referred to as husk, or psyllium husk. The milled seed mucilage is a white fibrous material that is hydrophilic, meaning that its molecular structure causes it to attract and bind to water. Upon absorbing water, the clear, colorless, mucilaginous gel that forms increases in volume by tenfold or more.

Cultivation

The genus Plantago contains over 200 species. P. ovata and P. psyllium are produced commercially in several European countries, the former Soviet Union and India. Plantago seed, known commercially as black, French, or Spanish psyllium, is obtained from P. psyllium, also known as P. arenaria. Seed produced from P. ovata is known in trading circles as white or blonde psyllium, Indian plantago, or isabgol. Isabgol is the common name in India for P. ovata. it is known as Aspaghol in Pakistan, coming from the Persian asp and gul, meaning "horse flower", which is descriptive of the shape of the seed. India dominates the world market in the production and export of psyllium.

Plantago ovata is an annual herb that grows to a height of 30–46 cm (12–18 in). Leaves are opposite, linear or linear lanceolate 1 cm × 19 cm (0.39 in × 7.48 in). The root system has a well-developed tap root with few fibrous secondary roots. A large number of flowering shoots arise from the base of the plant. Flowers are numerous, small, and white. Plants flower about 60 days after planting. The seeds are enclosed in capsules that open at maturity.

The fields are generally irrigated prior to seeding to achieve ideal soil moisture, to enhance seed soil contact, and to avoid burying the seed too deeply as a result of later irrigations or rainfall. Maximum germination occurs at a seeding depth of 6 mm (1/4 in). Emerging seedlings are frost sensitive; therefore, planting should be delayed until conditions are expected to remain frost free. Seed is broadcast at 5.5 to 8.25 kg/hectare (5 to 7.5 lb/acre) in India. In Arizonan trials, seeding rates of 22 to 27.5 kg/ha (20 to 25 lb/acre) resulted in stands of 1 plant/25mm (1 inch) in 15 cm (6 inch) rows produced excellent yields. Weed control is normally achieved by one or two hand weedings early in the growing season. Control of weeds by pre-plant irrigation that germinates weed seeds followed by shallow tillage may be effective on fields with minimal weed pressure. Psyllium is a poor competitor with most weed species.

Plantago wilt (Fusarium oxysporum) and downy mildew (Peronospora alta) are the major diseases of Isabgol. White grubs and aphids are the major insect pests.

The flower spikes turn reddish brown at ripening, the lower leaves dry and the upper leaves yellow. The crop is harvested in the morning after the dew is gone to minimize shattering and field losses. In India, mature plants are cut 15 cm above the ground and then bound, left for a few days to dry, thrashed, and winnowed.

Harvested seed must be dried to below 12% moisture to allow for cleaning, milling, and storage. Seed stored for future crops has shown a significant loss in viability after 2 years in storage.

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References
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